Previous work in animal models suggests that inhalational anesthetic agents may accelerate Alzheimer's disease pathogenesis, but it is unclear to what extent this may happen in humans. Here, the investigators propose to measure Alzheimer's disease-related neural markers in the cerebrospinal fluid (CSF) of patients exposed to anesthesia while undergoing neurosurgical procedures that require lumbar drain placement. Patients will be randomized to either receive inhalation anesthesia with isoflurane or intravenous anesthesia with propofol.

CSF and blood samples will each be collected at the induction of anesthesia, and then again ten and twenty-four hours later. CSF samples will be assayed for amyloid beta, tau, and other Alzheimer's disease-associated markers; blood samples will be assayed for serum inflammatory markers and used for genotyping studies. These studies should clarify the effect of common anesthetic agents on Alzheimer's disease related neural markers.

Inclusion Criteria:

• age 18 and above
• seen in neurosurgical clinic, and scheduled for operative aneurysm repair or other neurosurgical procedure necessitating lumbar drain placement.
• ability to speak English.
• ability to understand consent forms, and to give informed consent.

Exclusion Criteria:

• age less than 18
• lumbar drain is not placed
• not eligible for one of the anesthetics (inhaled isoflurane or IV propofol)
• inmate of a correctional facility (i.e. prisoners).
• pregnancy. Pregnancy is ruled out as standard of care before cranial surgery, based on clinical history and/or HCG testing